The presence of small amounts of fluoride in drinking water is commonly recognized to have a pronounced effect on reducing the incidence of dental caries in the permanent teeth of children. Fluoride salts have been introduced into public water supplies in many communities but this method of prophylaxis is not available to large numbers of people whose drinking water is obtained from fluoride deficient sources or where the addition of fluoride to common public water sources is not acceptable or permitted.
In 1950 Muhler et al. reported that stannous fluoride was more effective than 31 other compounds in preventing decalcification of powdered enamel in the laboratory. Radike and Muhler (1953) found that stannous fluoride reduced caries in hamsters by 51.2% in a topical and drinking water study while similar treatment with sodium fluoride resulted in only 26.3% reduction. Twenty years later, Radike et al. demonstrated the efficacy of a mouth rinse containing 250 ppm fluoride derived from stannous fluoride and in 1974, Corcoran reported that a stannous fluoride tablet yielding 200 ppm fluoride was effective as a caries prophylactic agent.
Limitations on the availability of fluoride therapy by means of the common water supply or by professional treatment has lead to extensive efforts to incorporate fluoride salts in dentrifices for use in the home. Toothpaste, however, often falls short of its cavity fighting mission because tooth brushing does not always reach the back teeth and the interproximal surfaces between teeth. It has been shown that 70% of all cavities occur in these areas.
Stannous fluoride is known to be subject to both oxidation and hydrolysis in aqueous solution to form the sparingly soluble stannous hydroxide which gives the solution a cloudy appearance and which is ineffective as an anti-caries agent. It is therefore not possible to formulate a stable aqueous stannous fluoride product and mouth rinse containing stannous fluoride must be used in a freshly prepared form.
Effervescent tablets which contain stannous fluoride were known prior to the present invention. For example, Welsh et al. in U.S. Pat. No. 3,518,343 shows water soluble tablets made by preparing an effervescent couple, a tableting lubricant and an antimicrobial substance which can optionally contain stannous fluoride. The effervescent couple includes a solid acid such as malic, fumaric, tartaric, itaconic, maleic, citric or mesaconic acid, and a solid base such as an alkali or alkaline earth carbonate or bicarbonate which, when dissolved in water, react to produce effervescence. One example of this patent discloses a stannous fluoride tablet employing citric acid and sodium bicarbonate in a weight ratio of about 2:3 as the effervescent couple.
It is the object of this invention to provide an effervescent tablet which will maintain the chemical integrity of the stannous fluoride anti-caries agent and rapidly dissolve in water to provide a stannous fluoride mouthrinse having a superior anti-caries potential. This and other objects of the invention will become apparent to those skilled in the art from the following detailed description.